1. Field of the Invention
The present invention relates to a centrifugal fan driven by a direct-current motor of the electronic commutation type.
2. Description of the Prior Art
Fans of this type usually have a volute or spiral housing which forms an air diffuser. Within said housing is mounted a blade-wheel or impeller which is coupled for rotation with the shaft of an electronic-commutation d.c. motor. The fan housing is provided on one side with a central air inlet and on the other side with a disk for closing the housing, said disk being provided with an opening through which the shaft passes on the side remote from the air inlet. The fan motor is placed within a protective casing which has a generally cylindrical shape and is adjacent to the outer face of the housing closure disk.
Since the motor is of the electronic commutation type, the electronic circuit for controlling the motor has to be included in the above-mentioned protective casing. This electronic control circuit makes it possible in particular to produce commutation or switching of the current direction within the stator windings or permits alternate supply of these windings as a function of the angular position of the rotor which is in turn controlled and supplied by a stationary position sensor. In the majority of instances, this sensor is a magnetic transducer such as a Hall-effect generator and is controlled by the permanent magnet constituting the rotor of the motor.
The presence of these electronic components mounted on a printed-circuit board makes it necessary to increase the dimensions of the protective casing to an appreciable extent or to associate with this latter an auxiliary casing which contains at least part of the electronic components just mentioned. It is also necessary in this case to provide two printed-circuit boards since the aforementioned position sensor must be mounted in the immediate vicinity of the rotor, which complicates the electrical connections and increases the construction cost. In all cases, the result thereby achieved is an increase in overall size of the centrifugal fan. This may prove highly objectionable in applications in which the space available for installation of said fan is limited.
Furthermore, the installation of the electronic components within the casing or in the vicinity of this latter and therefore in proximity to the motor increases the temperature elevation of these components, with the result that it is found necessary to overdimension the space required for this installation in order to ensure suitable ventilation of the control circuit.
British Pat. No. GB-A-1,345,585 describes an electric machine having an electronically-controlled circuit which is placed in the airstream of a tangential fan. The circuit components which are in direct contact with the air flow are liable to be damaged by any foreign bodies carried by this air flow.
U.S. Pat. No. 4,315,343 describes a suction motor having a volute with an axial air intake. This motor is of a conventional brush design and does not present any problem of cooling of electronic components.
One aim of the present invention is thus to propose a centrifugal fan of the aforementioned type which is distinctly more compact than any fans of known types and which also offers highly efficient ventilation of the electronic control circuit of the motor, thereby achieving enhanced reliability and longer service life of the motor.
A further aim of the present invention is to achieve an appreciable improvement in commutation control of the fan motor by placing the magnetic sensor at a greater distance from the motor and providing a sensor control track which is separate and distinct from the rotor magnet of said motor.